The authors have declared that no competing interests exist.
Conceived and designed the experiments: TG SW. Performed the experiments: TG LG. Analyzed the data: TG BH YP. Contributed reagents/materials/analysis tools: LC ZN RL YX. Wrote the paper: TG.
The retinoic acid receptor beta2(RARβ2) is a type of nuclear receptor that is activated by both all-trans retinoic acid and 9-cis retinoic acid, which has been shown to function as a tumor suppressor gene in different types of human tumors. Previous reports demonstrated that the frequency of RARβ2 methylation was significantly higher in prostate cancer patients compared with controls, but the relationship between RARβ2 promoter methylation and pathological stage or Gleason score of prostate cancer remained controversial. Therefore, a meta-analysis of published studies investigating the effects of RARβ2 methylation status in prostate cancer occurrence and association with both pathological stage and Gleason score in prostate cancer was performed in the study. A total of 12 eligible studies involving 777 cases and 404 controls were included in the pooled analyses. Under the random-effects model, the pooled OR of RARβ2 methylation in prostate cancer patients, compared to non-cancer controls, was 17.62 with 95%CI = 6.30–49.28. The pooled OR with the fixed-effects model of pathological stage in RASSF1A methylated patients, compared to unmethylated patients, was 0.67 (95%CI = 0.40–1.09) and the pooled OR of low-GS in RARβ2 methylated patients by the random-effect model, compared to high-GS RARβ2 methylated patients, was 0.54 (95%CI = 0.28–1.04). This study showed that RARβ2 might be a potential biomarker in prostate cancer prevention and diagnosis. The detection of RARβ2 methylation in urine or serum is a potential non-invasive diagnostic tool in prostate cancer. The present findings also require confirmation through adequately designed prospective studies.
Prostate cancer is the most commonly diagnosed noncutaneous neoplasia in the world. The disease predominantly affects men after the 6th decade of life and is associated with considerable morbidity and mortality
Recently, methylation of CpG islands within the promoter and/or 5′ regions of genes is recognized as a common alteration in cancer-related genes often associated with partial or complete transcriptional disruption
The RARβ2 is mapped to chromosomal region 3p24 (−477/+392, GenBank accession numbers S82362 and M96016), which is expressed in most tissues and has been shown to function as a tumor suppressor gene in lung, breast, and gynecological neoplasia
To date, RARβ2 methylation has been proved in a number of individual studies, which is detected not only in tissue samples but also in urine and serum samples. The prognostic value of RARβ2 methylation status in prostate cancer patient's diagnosis and the relationship between RARβ2 methylation and pathological stage of prostate cancer and Gleason score remains unclear. Therefore, a systematic review was performed of the literature with meta-analysis to obtain a more accurate evaluation of the role of RARβ2 methylation in prostate cancer management.
Studies were identified via an electronic search of PubMed and Google Scholar using the following key words: prostate cancer, PCa, retinoic acid receptor β2, RARβ2, RARbeta2, methylation. We also manually searched the references of these publications in order to retrieve additional studies. Only those published as full-text articles and in English were included as candidates. The search updated on 28, December,2012.
Studies were selected for analysis if they met the following criteria: 1) they were original epidemiological studies on the correlation between RARβ2 promoter methylation and the prognosis of prostate cancer patients; 2) RARβ2 methylation status was examined using methylation-specific PCR (MSP) or quantitative MSP (QMSP); 3)the subjects in every study comprised patients and non-cancer controls; 3) studies should be with full text not only abstracts for relevant information extraction; 4) when the same patient population reported in several publications, only the most recent report or the most complete one was included in this analysis to avoid overlapping between cohorts; 5) the numbers of patients and controls in each study should be more than 5 respectively.
For each eligible study, we collected information regarding authors, year and source of publication, country of origin, inclusion criteria, exclusion criteria, pathological stage, Gleason score, RARβ2 methylation frequencies in non-cancer controls and patients of prostate cancer and the method for methylation detection. All included studies used non-cancer people as a control group, though some of them did not provide the definition of non-cancer. In studies defining non-cancer people, there are two definitions: (1) normal healthy person; (2) people with benign hyperplasia prostate. Since it is impossible to redefine non-cancer people on a unified standard, we combined non-cancer people in our meta-analysis according to their original group in each individual study. Of these studies, pathological stage ≤ T2 was defined as low-stage, and pathological stage ≥ T3 was defined as high-stage which were defined by clinical differentiation. Gleason score≥7 was defined as high-GS and Gleason score≤6 was defined as low-GS. The final eligible articles selected for further meta-analysis were evaluated independently by two reviewers. Minor discrepancies were resolved by the authors' discussion.
The foremost analysis examined the differences in the frequency of RARβ2 methylation between prostate cancer patients and non-cancer people by odds ratio (OR) with the corresponding 95% CI. Moreover, the strength of association between RARβ2 methylation and patients' pathological stage and tumor Gleason score were also assessed by OR with the corresponding 95% CI. To assess heterogeneity across the studies, the statistics analysis for heterogeneity was performed
According to our inclusion criteria, a total of 12 eligible studies
First author | Year | Location | material | Patient and control | Method | RARβ2 (M/U)b | Pa(M/U)b | GS(M/U)b | |||
case | control | Low-gradec | High-grade | Low-GSd | High-GS | ||||||
Dumache R | 2012 | Romania | blood | 91/94 | QMSP | 89/91 | 10/94 | - | - | - | - |
Bastian PJ | 2007 | Germany | tissues | 78/30 | MSP | 56/78 | 1/38 | 32/47 | 24/31 | 30/48 | 26/30 |
Rouprêt M | 2007 | UK | urine | 95/32 | QMSP | 59/95 | 1/32 | - | - | 28/55 | 31/40 |
Hanson JA | 2006 | USA | tissues | 5/5 | QMSP | 4/5 | 0/5 | - | - | 3/18 | 8/20 |
Henrique R | 2006 | USA | tissues | 30/30 | QMSP | 26/30 | 6/30 | 18/20 | 2/10 | 14/15 | 13/15 |
Hoque MO | 2005 | USA | urine | 52/91 | QMSP | 18/52 | 8/91 | 7/24 | 11/28 | 11/24 | 7/28 |
Jerónimo C | 2004 | USA | tissue | 118/30 | QMSP | 115/118 | 7/30 | - | - | - | - |
Karen Woodson | 2004 | USA | tissue | 24/11 | MSP | 18/24 | 0/11 | - | - | 11/35 | 7/9 |
Jingmei Zhang | 2004 | USA | tissue | 50/2 | MSP | 42/50 | 0/2 | - | - | 14/18 | 28/32 |
Yamanaka M | 2003 | Japan | tissue | 109/36 | MSP | 85/109 | 0/36 | 29/39 | 56/70 | 33/47 | 52/62 |
Maruyama R | 2002 | USA | tissue | 101/25 | MSP | 54/101 | 1/25 | 12/26 | 22/34 | 11/36 | 44/65 |
Nakayama T | 2001 | Japan | tissue | 24/10 | MSP | 20/24 | 0/10 | - | - | - | - |
MSP, methylati on specific PCR; QMSP, quantitative methylation specific PCR. aP pathologic stage; bRARβ2 methylated/RARβ2 unmethylated; cpathologic stage≤ T2 was defined as low-stage and pathologic stage≥ T3 was defined as high-stage; dGleason score≤6 was defined as low-GSand Gleason score≥7 was defined as high-GS.
In general, the frequencies of RARβ2 methylation were tested in 12 reliable studies. The main results were summarized in
Variables | pa | OR | 95% CI | Heterogeneity | |||||||||
X2 | P | I2 | |||||||||||
RARβ2 | |||||||||||||
total | 12 | 63. 44 | 23.94–168.11 | 33.47 | 0. 001 | 67.1% | |||||||
total (trim-and-fill) | 12 | 17.62 | 6.30–49.28 | 85.27 | 0.001 | - | |||||||
material | |||||||||||||
Non-tissue | 3 | 46. 76 | 2.68–817.26 | 23. 18 | 0. 001 | 34.3% | |||||||
Tissue | 9 | 67.85 | 33. 75–136.42 | 5.11 | 0. 746 | 0. 0%b | |||||||
method | |||||||||||||
QMSP | 6 | 47. 10 | 10.59–209.53 | 27.56 | 0. 001 | 81.9% | |||||||
MSP | 6 | 89. 15 | 31.93–248.90 | 2.05 | 0. 842 | 0. 0%b |
Number of comparisons.
Between group heterogeneity not calculated; only valid with inverse variance method.
Variables | p |
OR | 95% CI | Heterogeneity | ||
X2 | P | I2 | ||||
stage | 5 | 0.67 | 0.40–1.08 | 1.75 | 0. 782 | 0.0% |
Gleason score | 8 | 0. 54 | 0.28–1.04 | 17.91 | 0. 012 | 60. 9% |
Number of comparisons.
Between group heterogeneity not calculated; only valid with inverse variance method.
Sensitivity analysis revealed that 11 independent studies were the main source of heterogeneity
As shown in
Each point represented a separate study for the indicated association. Logor natural logarithm of OR, horizontal line mean effect size. A: Begg's funnel plot of publication bias test. B: Begg's funnel plot of publication bias test after trim-and-fill method.
The results of our systematic review showed that RARβ2 methylation in prostate cancer was associated with tumor risk as either detected in urine, serum or tissue by MSP or QMSP. However, the RARβ2 methylation was not associated with increased risk for developing pathological stage or Gleason score of prostate cancer in comparison between RARβ2 methylated bladder cancer patients and unmethylated patients.
Hypermethylations of the RARβ2 gene having been reported in many studies declared that the frequency of RARβ methylation was found to be significantly higher in patients group compared with controls
However, Carmen Jerónimo's study suggested that RARβ2 methylation levels correlated with pathological tumor stage but not with Gleason score
Early diagnosis of prostate cancer currently relied on trans-rectal ultrasound guided needle biopsy (10 to 12 cores) in men with increased total PSA (greater than 4.0 ng/ml) and/or abnormal DRE findings
Cancer is not a single cell disease. Aberrant cancer cells and their interactive microenvironment are needed for cancer to progress to androgen independence and distant metastasis
RARb2 might be silenced not only by DNA methylation but also by histone deacetylation. Acetylation and deacetylation on lysine residues of histone amino-terminal tails had profound effects on gene transcription
In conclusion, our meta-analysis suggested that detection of RARβ2 methylation might be a potential biomarker diagnostic tool in prostate cancer. The detection of RARβ2 methylation in urine or serum is a potential non-invasive diagnostic tool in prostate cancer. It is necessary to conduct large sample size studies of the association between RARβ2 methylation and prostate cancer risk, eventually leading to our better understanding.